feat(contrib/ec2): use ephemeral drive for etcd journal
feat(contrib/ec2): use ephemeral drive for etcd journal

The changes in #2803 unfortunately don't address all of the etcd-related
performance issues. Provisioning Deis can still cause etcd timeouts.
Moving the etcd journal to the unused ephemeral disk allows etcd to
write to a very fast disk, resulting in fewer etcd/fleet issues.

refs #2793
refs #2506

deis/workflow,deis/workflow,deis/workflow